[postgis-devel] short question

[Nicklas Avén]

My first post was just about how to move the information internally that an empty geometry should be returned, from my function lw_dist2d_distanceline in measures.c to function LWGEOM_shortestline2d in lwgeom_functions_basic, when the expected return is LWLINE But I have realised that the thing is a little bit bigger because I out to return the right type externally too.Otherwise it will violate constraints if people tries to put the result in a table. Is this solved in other functions like st_union or st_difference? /Nicklas  

2009-11-22 Paul Ramsey wrote:

You are constructing empty geometries? Why? (Or is this a question of
>curiosity?)
>
>From an API PoV we should probably make some functions to do this, but
>the details are, generally, an LWGEOM with a POINTARRAY that has
>npoints = 0. Or, for collections, a collection with ngeoms = 0. I
>believe I also consider LWGEOMs with a null POINTARRAY or a null
>**geoms to be empty, but I'd have to confirm. The exact way of
>representing empty things was never fully documented
>
>P.
>
>On Sat, Nov 21, 2009 at 4:13 PM, Nicklas Avén
> wrote:
>> OK
>>
>> But what to send as empty when LWLINE or LWPOINT is wanted, not
>> LWCOLLECTION.
>> internally I mean.
>> /Nicklas
>>
>> 2009-11-22 Paul Ramsey wrote:
>>
>> No, bad idea. Empty geometries have a type. There's 'POLYGON EMPTY',
>>>'LINESTRING EMPTY', etc, etc, etc.
>>>
>>>P.
>>>
>>>On Sat, Nov 21, 2009 at 2:04 PM, Nicklas Avén
>>> wrote:
>>>> is type 0 for LWGEOM occupied by anything or could it be an idea to use
>>>> it
>>>> for empty geometries.
>>>> Then it would be easy to create any emtpy geometry. Like a generic empty
>>>> geometry.
>>>>
>>>> Or is there another way that I have missed.
>>>>
>>>> When I have identified the empty geometries, in shortestline and it
>>>> buddies
>>>> I need to communicate that an empty geometry should be returned and the
>>>> datatype is LWLINE and LWPOINT for st_closestpoint. I'm tempted to just
>>>> make
>>>> an LWGEOM with type 0. Is it a bad idea.
>>>>
>>>> #define EMPTY 0
>>>> #define POINTTYPE 1
>>>> #define LINETYPE 2
>>>> #define POLYGONTYPE 3
>>>> and so on
>>>>
>>>> /Nicklas
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